The present invention relates to film materials for the utilization in stretch-wrapping techniques in which the film is wrapped about the goods and serves as an exterior covering for same.
Thermoplastic stretch-wrapping materials have found particular commercial use in the overwrapping of goods or pallets of goods. In general, a transparent thermoplastic film is stretched about a pallet containing individual elements or packages of elements during which the pallet of materials is also unitized for ease of handling. Due to the transparent nature of the thermoplastic films involved, the contents of the pallet are visible. Furthermore, by using stretchable thermoplastic film instead of strapping, where the strapping materials are metallic or polymeric, a considerably safer situation is present both in the process of wrapping the materials, while the unitized pallet, etc. is in storage, and very importantly during removal of the film. Particularly, when strapping is utilized to unitize a pallet of goods, or packages of goods, a plurality of straps are passed around a small percentage only of the goods, and are tightened thereabout to secure the goods or packages to the pallet. In order to unitize the pallet with strapping techniques, it is necessary to tension the strapping material to a point where oftentimes certain of the containers are crushed by the strapping force. Moreover, while obviously the strapped packages or goods may be viewed on the pallet, they are also unprotected from the elements and may be damaged or become dirty by exposure to the elements. Upon removal of the tensioned straps from the pallet, there is constantly a danger that upon cutting the tensioned strap, an end of same will strike and injure a nearby individual. Still further, disposal of removed strapping, whether metal or polymeric presents a significant problem.
Conversely, with thermoplastic stretch-wrap materials, where the goods are covered with multiple wraps, the wrapping material totally covers the sides of the goods for the entire height of the pallet or goods and if also wrapped about the pallet in a head to toe operation, totally encapsulates the goods thereon. Since the wrapping material conforms itself to the outer edges and extremities of the packages or goods, the wrapping film must be resistant to tear and burst for successful use. Moreover, with a pallet so wrapped, even in the event of a tear or puncture of the wrap film, the force of the packaging is distributed over the height of the pallet as opposed to being concentrated as with a single band of strapping material such that there is no danger of the material becoming a possible lethal projectile in the event of rupture.
Stretch-wrapping materials have been heretofore utilized successfully in the wrapping of goods or pallets of materials where either the goods or the pallet are rotated past a wrapping station with the film maintained under appropriate stretch or tension conditions, or where a film holder is moved about the goods or pallet, again with the film under stretch or tensioned conditions as appropriate for the particular arrangement. The wrap may be either flat or spiral, depending upon the width of the packaging material, the size of the pallet and the like, and once wrapping is complete, an end of the film may be appropriately secured to a prior film wrap layer or layers by tape, adhesives, cling character of the film or the like.
In general, stretch films employed in the prior art have included films manufactured from polyethylene, polyvinyl chloride, ethylene vinyl acetate and various copolymers in both single and multiple layer films.
As alluded to in part above, physical characteristics of stretch-wrap films are highly important in the overall success of use of the film. Particularly important properties include the resistance of the film to puncture, such as might be occasioned by the film wrapping around a sharp or protruding edge or corner of a product where a high amount of pressure may be involved over a relatively small surface. Likewise, other important physical properties of wrap films include elongation, clarity, toughness and resistance to tear, melt index, density, haze, and cling. For example, if during use, a rip or tear occurs along an edge of a film and extends inwardly therefrom, it is highly important that the film resist enlargement of the tear or rip across the entire width of same.
One example of a prior art thermoplastic stretchwrap film is set forth in U.S. Pat. No. 4,399,180 to Briggs et al. Briggs et al. disclose a three-layer thermoplastic film in which the three layers are coextruded and in which a core or inner layer, includes ethylene copolymerized with a minor amount of at least one alpha-olefin having 4 to 10 carbon atoms and two exterior or skin layers which include highly branched low density polyethylene.
Another example of a prior art stretch-wrap film is a co-extruded three-layer film in which the core layer is ethylene copolymerized with octane, and the skin layers are ethylene copolymerized with 1-butene. While the just-mentioned stretch-film has enjoyed commercial success, certain homogenity problems have been experienced with same as will be alluded to hereinafter which led to the possibility of weak spots in the film.
In the commercial production of co-extruded thermoplastic wrap films, once the basic film product has been produced and is in the process of being wound into roll form, the film is normally trimmed along each outer edge if the film width is to be that being extruded. Alternately, the film can be slit at desired widths with different rolls of films of the same or different width being simultaneously formed as the film is being produced. In either case, waste film is produced.
In a conventional commercial situation, it is highly desirable if not necessary from an economic standpoint, to recycle the just described waste film as opposed to discarding same. Conventionally, the waste film is collected, chopped up and reintroduced to one of the extruders wherefore it is reused in the production of the thermoplastic stretch-wrap film. Obviously, however, the scrap film includes all of the various layers, whereby different polymers are present. When the different polymers are reintroduced to the extruder, normally into the core layer extruder, the core layer then ceases to be pure and, in fact, becomes a hybrid with the ultimate composition of same being determined by the amount of scrap or recycled material added to the extruder along with the virgin material. It is this recycling of scrap material that is believed to have created homogenity problems with the film defined above. Particularly, with an ethylene-octene core layer and ethylene-butene skin layers, the ethylene-butene components of the recycled material may become incompatible or nonhomogeneous with the ethylene-octene core material leading to the possibility of imperfections or weak spots in the ultimate co-extruded film.
The film of the present invention affords a technically improved stretch wrap material with quite good physical properties while not possessing the homogenity problems noted above. The stretch wrap film of the present invention thus represents an improvement over prior art films for such purpose and is neither taught nor suggested thereby. Exemplary of additional prior art are U.S. Pat. Nos. 4,418,114 to Buggs et al; 4,297,411 to Weiner; 4,125,662 to Waiver et al.; and 4,588,650 to Mientus et al.